The present invention relates to a sliding bearing apparatus having an excellent resistance to fretting.
In recent years, for the purpose of weight-saving or the like, a housing to which a sliding bearing is mounted is designed to have a thin thickness or to be made of an aluminum alloy, so that the rigidity thereof is reduced. Thus, in the housing, small, repetitive strains are apt to occur easily in correspondence with dynamic loads applied thereto. For example, in the bearing housing such as a large end portion of a connecting rod and a main bearing portion in an engine for a motor car, since the weight saving design explained above is adopted, relative micro-collisions and/or micro-slips occur between the inner, peripheral surface of the bearing housing and the rear face of the sliding bearing mounted on the inner face of the bearing housing in correspondence with the repetitive strains of the bearing housing, so that there occurs such a state as a damage due to the fretting abrasion is apt to be caused.
Conventionally, as a countermeasure to address the problem of the fretting, there has been known a technique of coating a resin material having an excellent lubricity such as, for example, a polytetrafluoroethylene (PTFE) on the rear face of the sliding bearing, or applying a metal plating such as a copper, a nickel or the like thereto.
In the sliding bearing apparatus in which the PTFE is coated, there can be obtained an effect of preventing the fretting from occurring at an early stage under the operation of the sliding bearing. However, the PTFE is apt to be worn away, so that there is a problem that it lacks the reliability insofar as the long-term resistance to fretting is concerned. Further, in the sliding bearing apparatus in which the plating layer of a metal such as copper, nickel or the like is applied, an adhesion phenomenon is apt to occur between the metal plating layer and the housing, so that there is another problem that the satisfactory resistance to fretting can not be obtained.
The present invention is achieved by taking the matters explained above into consideration, and an object of the invention is to provide a sliding bearing apparatus in which a layer provided for the purpose of preventing a fretting from occurring hardly causes the abrasion or the adhesion and in which an excellent resistance to fretting can be maintained for a long period of time.
According to the first aspect of the invention, there is provided a sliding bearing apparatus comprising: a sliding bearing having a back metal layer provided with an inner face and a rear face, and a bearing alloy layer bonded to the inner face of the back metal layer; a housing having an inner face onto which the sliding bearing is fitted, the rear face of the back metal layer and/or the inner face of the housing being provided with the layer of a ceramic material bonded thereto. Since, in general, ceramics has low coefficient of friction and are hardly adhered, they have superior resistance to fretting. Further, they are hard in hardness and are hardly worn, it is possible to maintain an excellent resistance to fretting for a long period of time.
According to the second aspect of the invention, there is provided a sliding bearing apparatus as set forth in the first aspect in which apparatus the ceramic material is selected from the group consisting of a nitride, a carbide, an oxide, a boride, a sulfide and a fluoride.
In this case, the ceramics is inferior in thermal conductivity. Thus, in a case where the layer of the ceramic interposed between the sliding bearing and the housing is thick in thickness, the heat dissipation from the sliding bearing to the housing is suppressed, so that the temperature of the sliding bearing is raised unfavorably. However, when the thickness of the layer of the ceramic is in the range of 0.05 to 5 xcexcm, the effect thereof for dissipating the heat can be obtained.
That is, according to the third aspect of the invention, there is provided a sliding bearing apparatus as set forth in the first aspect in which apparatus the thickness of the ceramic layer is in the range of 0.05 to 5 xcexcm.
In prior arts, the thickness of the PTFE layer inferior, similarly to the ceramic materials, in thermal conductivity is 30 xcexcm, and the thickness of the metal plating layer such as the copper, the nickel or the like is about 5 xcexcm. In comparison with these cases of the prior arts, the thickness of the ceramic layer is thin in thickness, so that it is possible to enhance the heat dissipation of the sliding bearing and to thereby improve the bearing properties of the sliding layer.